1. Field of the Invention
The present invention relates to headphones. More particularly, the present invention relates to a headphone of an auricle insertion system (so-called inner ear-type headphone) so that a housing thereof is inserted into an auricle and secured therein when the headphone is in use.
2. Background of the Invention
Headphones of so-called auricle insertion type have hitherto been proposed as described in U.S. Pat. Nos. 4,736,435, 4,429,194 and 4,646,872, for example. The conventional headphone of this auricle insertion type is arranged as shown in FIGS. 1 and 2. FIG. 1 is an exploded perspective view of such conventional headphone, and FIG. 2 is a perspective view showing the headphone shown in FIG. 1 is in its assembled state. In FIGS. 1 and 2, reference numeral 1 designates a housing. The housing 1 incorporates therein a speaker unit 3 to which signal lines 2a, 2b are connected. The speaker unit 3 is inserted from an opening portion 1b of the housing 1 and accommodated within the housing 1 so as to expose its diaphragm 4 from the opening portion lb. The speaker unit 3 has a small diameter, e.g., ten-odd millimeters sufficient so that it can be inserted into an auricle and secured therein. The diaphragm 4 provided in front of the speaker unit 3 is driven by a magnetic flux generated from a magnetic circuit 5 provided at the rear portion of the speaker unit 3. More specifically, the diaphragm 4 is connected with a bobbin around which there is wound a voice coil to which an audio signal is supplied via the signal lines 2a, 2b. The bobbin and the diaphragm 4 are vibrated by a cooperation of a magnetic flux generated from a magnet provided within the magnetic circuit 5 disposed near the voice coil and an alternating magnetic flux generated by the voice coil on the basis of the audio signal supplied to the voice coil.
The two signal lines 2a, 2b are led out from a projecting portion 1a formed at the rear portion of the housing 1 as a single signal line 2. To the end portion of the signal line 2 is connected a plug (not shown) that is inserted into a headphone jack serving as an audio signal source. Although FIG. 1 or 2 shows only one headphone, a stereophonic-type headphone needs a pair of right and left headphones, each of which has the housing 1 thus arranged.
With the above-mentioned structure, a reproduced sound is radiated forwardly on the basis of the vibration of the diaphragm 4 of the speaker unit 3. A protector 6 having a number of apertures 6a of relatively large diameters is disposed so as to wholly cover the front surface of the diaphragm 4. This protector 6 is formed of a plate-shaped member having a relatively large strength, such as a stainless steel plate or the like to protect the diaphragm 4 or the like from being damaged when a pressure is applied thereto from the outside.
A grill 7 is disposed on the front surface of the protector 6. The grill 7 is made by forming a metal mesh of metal wires into a curved circular mesh structure by a press work. The grill 7 is disposed on the front surface of the protector 6 in order to prevent the speaker unit 3 from being smudged by dusts or the like entered from the outside.
A rubber ring 8 covers the headphone from the grill 7 to the housing 1. The rubber ring 8 has an opening portion 8a bored through its predetermined position so that, when this headphone is assembled as a product, the grill 7 is exposed only from this opening portion 8a. A reproduced sound is output from this opening portion 8a. The rubber ring 8 is provided in order to prevent the reproduced sound output from the headphone from being leaked to the outside of an auricle, i.e., to prevent a so-called sound leakage. The opening portion 8a is smaller than the opening portion 1b of the housing 1.
The reason that the grill made by treating the metal mesh by the press work is used as the grill 7 attached to the headphone is that the grill 7 thus formed has small meshes and is excellent in dust proof property. As a consequence, the headphone of this auricle insertion type can be reduced in thickness and can satisfactorily be used.
However, such grill made by treating the metal mesh by the press work is expensive and needs much time and labor when such grill is processed. More specifically, the expensive metal mesh in which metal wires are formed as a mesh structure is used as a material and much time and labor are required to form this metal mesh material into the curved circular grill by the press work. Particularly, when the metal mesh is cut into a circular grill, it is frequently observed that metal wires around the edge of the curved circular grill become loose. Therefore, it is unavoidable that a defectiveness of a fraction of the grill is increased.